eChapters

5.1. SEED AND SEED PRODUCTION

Origin of Plentiful Yield is the Seed - Parashara 400BC

Good Seed in Good Soil Yield Abundantly - Manu Smriti 200BC

Botanically seed is a matured ovule containing an embryo in arrested state of development with a food reserve (endosperm) and protective coat (seed coat). In albuminous seeds the endosperm is present eg. rice, wheat, castor (cereals). Whereas, exalbuminous seeds the endosperm is absent eg. onion and pea (pulses).

Types of fruit/ seed

4.1. PESTS OF FIELD CROPS

Insect pests are the major constraints limiting agricultural productivity growth. It is estimated that herbivorous insects eat about 26 percent of the potential food production. Emerging problems of insecticide and disease resistance, secondary pest outbreak and resurgence further add to the cost of plant protection. Annual crop losses due to insect pests and diseases in India are estimated to be 18 percent of the agricultural output. Main causes of emerging pest and disease are favourable prevailing weather condition, absence of natural enemies, abundant food supply, use of pesticides, use of fertilizers and irrigation.

PESTS OF RICE

Borers and Defoliators

3.1. INTRODUCTION TO PLANT BREEDING

What is Plant Breeding?: Plant breeding is an art and science which deals with changing genotypes of the plants, to adapt them to the service of human being. (or) The application of genetic and cytogenetics principles in crop improvement are called plant breeding.

Specific objectives of plant breeding: The main objectives of the plant breeding is to improve the characteristics of crop plants which are agronomically and economically desirable

Soil

Soil is a natural body of mineral and organic constituents differentiated into horizons usually unconsolidated, of variable depth which differs among themselves as well as from the underlying parent material in morphology, physical makeup, chemical properties and composition and biological characteristics (Whitney, 1982; Hilgard, 1892; Dokuchaiev, 1900 and Joffe, 1936).

According to Soil Science Society of America (SSSA, 1970) soil is the unconsolidated mineral matter on the surface of the earth that has been subjected to and influenced by genetic and environmental factors of parent material, climate (including moisture and temperature effects), macro and microorganisms and topography, all affecting over a period of time and producing a product, that is “SOIL” that differs from the material from which it is derived in physical, chemical, biological and morphological properties and characteristics. The unconsolidated mineral material on the immediate surface of the earth, that serves as a natural medium for the growth of plants.

Approaches of Soil Study

Pedological Approach : The origin of the soil, its classification and description are examined in Pedology. (From Greek word pedon means soil or earth). It is the study of soil as a natural body and does not focus on the soil’s immediate practical use.

Edaphological Approach: Edaphology (from Greek word edaphos means soil or ground) is the study of soil from the stand point of higher plants. Edaphologists consider the various properties of soil in relation to plant production.

Soil Science : The science dealing with soil as a natural resource on the surface of the earth, including pedology (soil genesis, classification and mapping) and the physical, chemical and biological and fertility properties of soil and these properties in relation to their management for crop production.

1.1. WEATHER AND TILLAGE

Weather : A state or condition of the atmosphere at a given place and at a given instant of time'

Climate : The generalized weather or summation of weather conditions over a given region during comparatively longer period

Meteorology : Greek word “Meteoro” means 'above the earth's surface' (atmosphere) and “logy” means “indicating science”. Branch of science dealing with that of atmosphere is known as meteorology

Agricultural meterology : Branch of applied meteorology or a branch of agriculture as it deals with agriculture

Coordinates of India : 8^o N and 37°N latitude; 68°E and 98°E longitude

Coordinates of Tamilnadu: 08°05' N and 13°35' N latitude; 76°15' E and 80°20' E longitude

Hydrosphere - water portion of the earth

Lithosphere - solid portion of the earth

Atmosphere - gaseous portion of the earth

Atmosphere : It is the colourless, odourless and tasteless physical mixture of gasses, which surrounds earth on all

A

Acervulus (pl. Acervuli)—A saucer-shaped, spore-producing body of a fungus embedded in host tissue.

Actinomycetes—Filamentous bacteria that produce several antibiotics and give soil its earthy smell.

Active ingredient: In pesticides, the chemical responsible for the desired effect.

Aggressiveness: Virulent forms of pathogen cause differing degrees of symptom severity.

Alternate Host—One of two kinds of plants on which a parasitic fungus (e.g., rust) must develop to complete its life cycle.

Anamorph—Asexual stage of a fungus.

Antagonism: The counteraction between organisms or groups of organisms.

The over emphasis on the use of chemical pesticides and their improper use by the farmers has led to several complications such as residue in food, feed, fodder, development of resistance, resurgence, secondary outbreak, etc. and above all, environmental pollution, leading to a condition known as Pesticide Treadmill characterized by the need to spray ever greater quantities of chemical pesticides. In 1962, Rachel Carson in her book ‘Silent Spring’ aroused worldwide concern about the excessive use of pesticides, which eventually led to the concept of Integrated Pest/Disease Management as an environmentally sound alternative to the sole use of chemicals.

The IDM Concept

In disease management, all the alternate control measures like cultural, biological, mechanical, resistant varieties, physical etc, are utilized in anintegrated manner in order to maintain the disease below economic injury level. If the disease increases and reaches the economic threshold level, pesticides are used to bring the disease down. This is concept of an Integrated Disease Management in which minimum pesticides are used keeping in view of agro- ecosystem. Actually, we do not go for 100 percent control in disease management rather the disease is allowed below which can be tolerated i.e economic threshold. This also provides opportunity for bioagent to survive, managing upon the diseases keeping them at certain equilibrium level. Thus, the Integrated Disease Management concept aims at managing the disease through all the available tactics with favorable economic, social and ecological consequences.

Plant diseases are a threat to world agriculture. Significant yield losses due to the attack of pathogen occur in most of the agricultural and horticultural crop species. More than 70% of all major crop diseases are caused by fungi . Plant diseases are usually handled with applications of chemicals. For some diseases, chemical control is very effective; but it is often non-specific in its effects, killing beneficial organisms as well as pathogens. Chemical control may have undesirable effects on health, safety and cause environmental risks. A promising method for protecting plants against diseases is constructing and employing pathogen-resistant cultivars. Although a number of resistant cultivars have been developed through breeding programs, these cultivars become obsolete in a short time due to the rapid evolution of the phytopathogens and the emergence of virulent forms capable to overcome the plant resistance. Breeders are often confronted with the issue of using a limited number of plants in their breeding programs, undesirable traits transferred together with the valuable resistance genes, and, in recent years, also with the depletion of potential gene sources. Control of diseases is a subject of great interest for biotechnologists. The most significant development in the area of varietal development for disease resistance is the use of the techniques of gene isolation and genetic transformation to develop transgenic resistance to fungal, bacterial and viral diseases. Improvements in genetic transformation technology have allowed the genetic modification of almost all important food crops like rice, wheat, maize, mustard, pulses and fruits. Genetic engineering technology has proved to be beneficial in managing viral and bacterial diseases in plants. The advances in gene engineering technologies and the understanding of the molecular nature of plant protection mechanisms have provided means for developing principally new strategies of plant disease control, in addition to the traditional approaches based on employing chemicals or classical breeding schemes. Biotechnology will enhance our understanding of the mechanisms that control plant’s ability to recognize and defend itself against disease caused by fungi. The integration of biotechnology with traditional agricultural practices will be the backbone for sustainable agriculture.

Proper selection of a fungicide and its application at the correct dose and the proper time are highly essential for the management of plant diseases. The basic requirement of an application method is that it delivers the fungicide to the site where the active compound will prevent the fungus damaging the plant. The fungicidal application varies according to the nature of the host part diseased and nature of survival and spread of the pathogen. The method which are commonly adopted in the application of the fungicides are discussed

1. Foliar or vegetative application
2. Soil application

INTRODUCTION

The use of chemical for protecting plants from the ravages of the pathogens is not an innovation of the 20th century. Chemicals have been used for over 200 years to protect plants against fungal diseases. At present about 150 chemicals belonging to different classes are used as fungicides in world agriculture. Most of the recommended treatments generally provide 90% or greater control of target diseses. Even when a crop has been grown from pathogen free soil and the crop seems superficially healthy, the use of fungicides in some circumstances become unavoidable. Resistant varieties of potato are attacked by late blight if rain occurs during tuber formation. To control this disease use of fungicides become vital to avoid any loss of the crop. Thus, even in the case of resistant varieties, judicious use of chemical protection will extend the life of resistance in the variety. For killing different groups of pathogens, different types of chemicals are required. The chemicals mainly used for controlling diseases are: fungicides for killing fungus, bactericide for killing barteria, nematicides for killing nematodes, and viricides for killing viruses.

INTRODUCTION

The current food crisis has put the agriculture production on a tight leash, not allowing the producers any lassitude whatsoever. Even though we have outgrown from our ‘ship to mouth existence’; our least negligence can torpedo our efforts to maintain the steady state of progress achieved in food grain production. Around 35% of what is produced is lost due to pest and diseases. In this situation, plant protection assumes significance. Unfortunately our plant protection regime begins and ends with pesticides. It is the default option in the plant protection menu and all the other options more or less remain defunct and unused. Even though, our major thrust areas of plant protection are promotion of Integrated Pest Management: ensuring availability of safe and quality pesticides for sustaining food production from the ravages of pests and diseases, streamlining the quarantine measures for accelerating the introduction of new high yielding crop varieties, besides eliminating the chances of entry of exotic pests; we remain largely insulated from these aspects in IPM.

With the Globolization and liberalization in International trade of plants and plant material in the wake of Sanitary and Phytosanitory (SPS) Agreement under WTO, the plant quarantine measures have become more imperative. Liberalization of trade policies have helped the world agriculture trade to prosper which is key sector for many countries like India whose economies are dependent on agrarian industry. But the likehood of the presence of disease/pest inherent in the import material can very well geopardize the trade. Activities are meant to help agricultural development and Plant quarantine service are charged with the responsibility of preventing the entry of hazardous pests, pathogens and weeds, but to deny entry of valuable genetic re-sources would be against national interest. These activities are meant to help agricultural development and they are complementary to each other and therefore are necessary, and we on our parts need to be fairly vigilant. As has been very truly said-An ounce of prevention is worth a pound of cure.

INTRODUCTION

Plant pathogens can spread rapidly over great distances, vectored by water, wind, insects, and humans. Across large regions and many crop species, it is estimated that diseases typically reduce plant yields by 10% every year in more developed nations or agricultural systems, but yield loss to diseases often exceeds 20% in less developed settings, an estimated 15% of global crop production.

Disease control is reasonably successful for most crops. Disease control is achieved by use of plants that have been bred for good resistance to many diseases, and by plant cultivation approaches such as crop rotation, pathogen- free seed, appropriate planting date and plant density, control of field moisture and pesticide use. However, the most attractive form of control is provided by disease resistance, for as long as it remains effective, it provides protection at no cost to the farmers or the community. So plant resistance is a highly useful strategy that can be applied in the control of diseases. It does not require any special action from growers and constitute cheap and practical input in the integrated disease management system. The use of resistant varieties cannot only ensure protection against diseases but also save the time, energy and money spent on other measures of control. In addition to these advantages, resistant varieties, if evolved, can be the only practical method of control of such diseases as viruses, phytoplasmas wilts, and rusts etc. in which chemical control is very expensive and impractical. In crops of low cash value, chemical and other methods of control are often too expensive to be applied. In such crops development of varieties resistant to important diseases can be an acceptable recommendation for the farmer.

Plant diseases need to be controlled to maintain the quality and abundance of food, feed, and fiber produced by growers around the world. Different approaches may be used to prevent, mitigate or control plant diseases. Beyond good agronomic and horticultural practices, growers often rely heavily on chemical fertilizers and pesticides. Such inputs to agriculture have contributed significantly to the spectacular improvements in crop productivity and quality over the past 100 years. However, the environmental pollution caused by excessive use and misuse of agrochemicals, as well as fear-mongering by some opponents of pesticides, has led to considerable changes in people’s attitudes towards the use of pesticides in agriculture. Today, there are strict regulations on chemical pesticide use, and there is political pressure to remove the most hazardous chemicals from the market. Additionally, the spread of plant diseases in natural ecosystems may preclude successful application of chemicals, because of the scale to which such applications might have to be applied. Consequently, some pest management researchers have focused their efforts on developing alternative inputs to synthetic chemicals for controlling pests and diseases. Among these alternatives are those referred to as biological controls.

INTRODUCTION

The Cultural practices which includes manipulation /or adjustment of crop production techniques have been as old as possibly agriculture itself. In early stages of agriculture development, the growers through their experiences and observations had known that repeated cultivation of a particular crop species or variety on a piece of land often resulted in crop sickness. By proper crop rotations they had been avoiding such sickness. As a matter of fact, in the present day agriculture, cultural practices are being considered as essential backup methods for plant disease management. Cultural practices often offer the opportunity to alter the environment, the condition of the host, and/or the behavior of the causal agent, to achieve economic management of disease. Most cultural practices used to control plant disease are preventive in nature. Integration of cultural practices, host resistance and pesticides or biocontrol agents may be necessary to provide options for controlling economically important plant diseases

PRINCIPLES

The principles involved in thermotherapy is that the pathogens present in seed material are inactivated or eliminated at temperatures nonlethal for the host tissues.The exact mechanism by which heat inactivates the pathogen is not fully understood. However, it is universally accepted that heat causes inactivation and not immobilization of the pathogen by heat. Thrate at which the pathogen is inactivated is determined by temperature, the higher the temperature, the faster is the inactivation.

INTRODUCTION

Plant diseases have caused severe losses to humans in several ways. Starvation and uprooting of families resulted from the Irish famine caused by potato late blight . A valued resource was lost with the virtual elimination of the American chestnut by chestnut blight. And direct economic loss such as the estimated one billion dollars lost in one year to American corn growers from southern corn leaf blight . Many plant diseases cause less dramatic losses annually throughout the world but collectively constitute sizable losses to farmers and can reduce the aesthetic values of landscape plants and home gardens.

The goal of plant disease management is to reduce the economic and aesthetic damage caused by plant diseases. Conventionally, this has been called plant disease control, but current social and environmental values believe “control” as being absolute and the term too rigid. More multifaceted approaches to disease management, and integrated disease management, have resulted from this shift in attitude. However, single, often severe, measures, such as pesticide applications, soil fumigation or burning are no longer in common use. Further, disease management measures are often determined by disease forecasting or disease modeling rather than on either a calendar or prescription basis. Disease management might be viewed as proactive whereas disease control is reactive, although it is often difficult to distinguish between the two concepts, especially in the application of specific measures.

Plant disease management practices rely on anticipating occurrence of disease and attacking vulnerable points in the disease cycle (i.e., weak links in the infection chain). Therefore, correct diagnosis of a disease is necessary to identify the pathogen, which is the real target of any disease management program. A thorough understanding of the disease cycle, including climatic and other environmental factors that influence the cycle, and cultural requirements of the host plant, are essential to effective management of any disease.

DEFINITION

Fore casting involves all the activities in ascertaining and notifying the grower of community that conditions are sufficiently favourable for certain diseases, that application of control measures will result in economic gain or on the other hand, and just as important that the amount expected is unlikely to be enough to justify the expenditure of time , energy and money for control. The above statement made explicit distinction between positive forecast and negative forecast and both have value for growers as well as society in general.

Positive forecast: Employs need based chemical sprays, provides adequate protection to crop and reduces damage to environment.

Negative forecast: Avoids unnecessary chemical sprays, no risk to the crop health and no disruption of environment.

CONCEPT

The word “epidemic” is derived from the greek word, epi= (on) and demons=(people) and in true sense applies to those disease of human being which appear very virulently among a large section of population. To carry the same sense in the case of plant diseases the term epiphytotic has been coined. an epiphytotic disease is one which occur widely but periodically. it may be present constantly in a locality but assumes severe form only on occasions. Of late, the term “epidemiology” has come to have a broad meaning within plant pathology. The term has been variously defined as the study of disease in populations; the study of environmental factors that influence the amount and distribution of diseases in population, and the study of either increase or decrease in the amount of disease in time, in space, or both.

Elements of An Epidemic

Generally, the elements of an epidemic are referred to as the “disease triangle”: a susceptible host, pathogen, and favorable environment. For disease to occur all three of these must be present. Where all three items get together there is disease. As long as all three of these elements are present disease can commence, an epidemic will only arise if all three continue to be present. Sometimes a fourth factor of time is added as the time at which a particular infection occurs, and the length of time conditions remain viable for that infection, can also play an important role in epidemics If all of the criteria are not met, such as a susceptible host and pathogen are present but the environment is not conducive to the pathogen infecting and causing disease, disease cannot occur.

Factors that affect the development of epidemics

INTRODUCTION

Variability in different organisms is common feature and is an important process for the continuity of life under stress conditions. Plant pathogens especially fungi, bacteria, virus and nematode show variations in their pathogenic potential (virulence) and physiological functions that support their survival and perpetuation in different environmental conditions. These variations may be largely due to genetic factors that may be conditioned by environmental factors. Various studies on genetic variability of microbial plant pathogens have shown that variations may occur in characters which affect their ability to infect host plants and also other characters that do not alter the pathogenic potential, but they may be concerned with their survival. Knowledge of variation in pathogenic characteristics is valuable in planning effective measures for disease management. In addition, development of resistant to fungicides has been a serious concern to growers, researchers as well as the administrators, since the decision to continue application or withdrawal of a fungicide can affect both the growers and industry.

Resistance to disease in a host plants is a condition in which the plant conquer the pathogen’s attack and thus suffers small or no injury. Resistant hosts prevent or slow the development and reproduction of the majority of pathogen propagules that they come into contact with. Different plants defend themselves in different ways. Each kind of plant, probably, employ different defense mechanism against each of the pathogens that attack it. The defense barriers erected by plants are a co-ordinated system of molecular, cellular and tissue-based responses to pathogen attack.

There are various mechanisms of defense used by plants. For convenience, such mechanisms can be considered under two broads heads;

1. Pre existing or passive defense (Defense present on or inside the plant since beginning)

a. Pre existing structural defense

b. Pre existing biochemical defense

2. Post infection or active defense (Defense in response to attack by the pathogen)

a. Post infection structural defense

b. Post infection biochemical defense